Applied Allelopathy: Effects of Daffodils On Other Species In Sustainable Agriculture and the Home Landscape

The purpose of this study is to investigate which plants can be grown successfully with daffodils as follow-up crops for small farmers or as plantings to cover senescing foliage of daffodil bulbs for landscapers.   Other investigators have shown that Narcissi spp. have allelopathic effects due to alkaloids they produce.  They identified Narciclasine, a compound isolated in the mucilage of Narcissus bulbs, as one cause of inhibitory effects on growth and plastid development in excised radish cotyledons.  In the present study, four varieties of Narcissi: N. tazetta ‘Paper-white’, N. jonquilla ‘Quail’, Narcissus ‘Ice Follies’, N. tazetta ‘Thalia’ were used.  Greenhouse and field experiments were conducted to evaluate the effects of leaf leachate or plant residue of Narcissus on  growth and development of landscape plants and herbs that included Antirrhinum nanum ‘Frosted Flames’ (snapdragon),  Callistephus chinensis ‘Powder-puff’ (Chinese aster) , Coleus scutellarioides ‘Dragon Sunset’ and ‘Volcano’ hybrids (Coleus), Cosmos sulphureus ‘Polidor’ (Cosmos), Ocimum basilicum ‘Genovese’ (basil), O. basilicum ‘Lettuce Leaf’ (basil),  Petroselinum neapolitanum (Italian parsley),  Zinnia elegans ‘Envy Double’ (Zinnia),  and Fragaria vesca ‘Mignonette’ (strawberry).   In pot studies germination of seeds of snapdragon, was reduced by 60 to 80% and delayed by 14 to 25 days when planted with N. tazetta ‘Paper-white’.  Leaf residues of N. jonquilla ‘Quail’ and N. ‘Ice Follies’ caused up to 50% stunting of  the Coleus varieties, and some chlorosis was observed in the leaf blades of C. scutellarioides.  In pots planted with N. jonquilla ‘Quail’ and N. ‘Ice Follies’ and placed outside the greenhouse, airborne weed seeds did not germinate in the undisturbed pots, compared to pots without Narcissus that had extensive weed growth.  In a field experiment co-planting of Narcissus with several of the summer annuals and herbs, the greatest effects were observed on basil.   Transplanted basil seedlings had reduced growth and  fresh weight in the presence of N. ‘Ice Follies’ and N. tazetta ‘Thalia’ bulbs, and several of the basil plants exhibited chlorosis.    Transplanted seedlings of Cosmos and Zinnia in the presence of Narcissus were slow to reach flowering stage when compared to the absence of Narcissus.  In field co-plantings, no negative effects were observed on Chinese aster, strawberry, and parsley.  The evidence indicates that Coleus and basil would not be suitable as follow-up planting after Narcissus spp.